Dissipation rates of dufulin residues in paddy, soil, and water determined by ultra-performance liquid chromatography coupled with photo-diode array detection

A sensitive and selective analytical method for dufulin detection was developed using ultra-performance liquid chromatography coupled with photo-diode array detection (UPLC-PDA). Dufulin analysis was carried out with 1l sample injection on BEH C18 column (50.0mmx2.1mm i. d., 1.7m film thickness) thermostatted at 40 degrees C with a mobile phase of methanol/water (58/42 by volume) at flow rate of 0.3mlmin(-1). Dissipation rates of dufulin in paddy plant, soil, water, and brown rice in three districts in China were studied using the method developed. Dufulin (30% WP) was applied at two dosages, 337.50g a. i. ha(-1) (recommended dosage) and 506.25g a. i. ha(-1) (1.5 times the recommended dosage) in experimental fields in Guizhou, Anhui, and Tianjin provinces in China. The limit of detection (LOD) and the limit of quantification (LOQ) of dufulin were 2.5 and 7.5g kg(-1), respectively. The average recoveries were 72.76-95.43, 97.84-101.7, 96.99-100.8, and 80.91-100.5% in paddy plant at four spiking levels (0.04, 0.20, 2.0, 50.4mgkg(-1)), in water at three spiked levels (0.0025, 0.025, 0.25mg l(-1)), in soil at three spiking levels (0.04, 0.13, 1.3mgkg(-1)), and in brown rice at four spiking levels (0.05, 0.20, 2.0, 10.0mgkg(-1)), respectively. Our results showed that half-lives of dufulin in paddy plant and water in the three districts were 7.7-11.3 and 2.1-4.8 days, respectively. At harvest, dufulin residues in brown rice samples collected 35 days after the last dufulin application at the recommended dosage were below 0.5mgkg(-1). Our results provided data to help establish appropriate application frequency and harvest intervals in the use of dufulin for rice pest control in China.